Effect of Thermal Treatments on Antioxidant Properties of Pumpkin Flesh and Their Stability during in-vitro Gastrointestinal Digestion
Keywords:Pumpkin, Phenolic compound, Carotenoids, Antioxidant activity, in-vitro gastrointestinal digestion
Flesh of pumpkin (Cucurbita maxima) is especially rich in carotenoids and phenolic compounds that exert antioxidant properties. In this study, two varieties of pumpkin, Srimuang (Thai variety with rough skin) and Kabocha (Japanese variety with smooth skin) were subjected to four different heat treatments including boiling (90 °C for 5 min), steaming (100 °C for 5 min) and hot air drying (60 °C for 16 h and 70 °C for 10 h). Uncooked samples were served as control. Results showed that rough skin pumpkin contained higher total phenolic content (TPC) and total carotenoid content (TCC) than smooth skin pumpkin and consequently, the higher antioxidant activities based on Ferric reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity. Among heat treatments, Drying at 70 °C of smooth skin pumpkin showed the strongest TPC and antioxidant activity base on FRAP and DPPH. In rough skin pumpkin, drying at 70 °C showed the highest TPC corresponding to the highest FRAP values. After boiling, TCC increased in rough skin pumpkin but, reduced to the lowest extent in smooth skin pumpkin. During in-vitro digestion, TPC slightly increased from oral, gastric to intestinal phase in all heat-treated samples. However, the corresponding antioxidant activities based on FRAP and DPPH were found to decrease on digestion. The exception as for DPPH values of heat treated smooth skin pumpkin that remained unchanged. Results showed the higher correlation among TPC, FRAP and DPPH of samples before digestion (r = 0.704–0.902, p < 0.01) than that of samples after digestion (r = 0.411–0.716, p < 0.01). The content of bioactive compounds depended not only on their concentration in pumpkin, but also processing conditions and gastrointestinal digestion which influenced their stability and consequently, changes in antioxidant activities.
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